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Cotton Population Dynamics: Influence of the Within-the-Row Spacing and Emergence Time¹

Dynamic and stochastic properties of cotton (Gossypium hirsutum L.) plant populations increase the difficulty of production management. The influence of four within-the-row plant spacings on beds spaced at 102 an (5, 20, and 40 cm, and random 7.5 to 10 cm) and three times of emergence (5, 7, and 9 days in 1973; 6, 8, and 10 days in 1974) on means and coefficient(s) of variability (CV) of plant height, number of main stem nodes, squares, and bolls were measured over time using the cultivar ‘Tamcot 788’. The CV values for each plant component varied with stage of development. The range of CV values was 16 to 31%, for plant height, 14 to 23% for number of main stem nodes, 30 to 187% for number of squares, and 36 to 270% for number of bolls. Emergence time exerted a significant influence on the CV values of all plant characters throughout the 1973 season and during the first 80 days in 1974. Plant spacing significantly affected CV values of squares and bolls at first square and peak bloom in 1973. In 1974 plant height was affected beginning at 86 days after emergence; number of main stem nodes, after 100 days; and number of bolls, after 93 days.

Mean plant height and number of main stem nodes was greatest for early emerging plants. The highest number of bolls at maturity was produced on the earliest emerging plants in 1973. The 5-cm plant spacing reduced the number of main stem nodes at maturity without affecting plant height in 1973. However, after midseason in 1974, plants spaced 5 cm were shorter and had fewer nodes than plants spaced 20 and 40 cm.

Plants experienced greater moisture stress in 1974 than in 1973. The CV values for plant height and main stem node number during 1974 for plants spaced at 5 cm increased as the season progressed, but did not change for plants spaced at 20 and 40 cm. CV values for main stem node number and plant height showed no seasonal trend in 1973.

Plant spacing and emergence time influenced the means and variabilities of plant components. The level of variability is different for each plant character and changes over time. An estimate of the true mean of a plant component over the season at the same confidence level would require adjustment of the sample size according to the variability changes.

Key Words: Plant height • Main stem node number • Number of squares • Number of bolls

² Agricultural engineer and agronomist, respectively, Southern Region ARS/USDA Texas A&M Research and Extension Center, Lubbock, TX 79401.

Received for publication September 7, 1976.

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